The present invention relates to an X-ray computed tomography apparatus, a dose calculation method, and a program thereof.
Generally, an X-ray CT apparatus has functions that calculate and display a dose value for an imaging target based on the size of the imaging target or predetermined scan conditions.
The dose calculation uses dose measurement reference values resulting from actually imaging columnar acrylic phantoms. Two types of phantoms are used as the reference. One type of phantom is 16 cm in diameter and is intended for an infant or adult head. The other is 32 cm in diameter and is intended for an adult body.
Generally, the X-ray CT apparatus selects the measurement reference value for a correspondingly sized phantom based on information about a subject such as distinction between an adult and an infant and imaging locations. The X-ray CT apparatus multiplies the measurement reference value by a factor (weight) based on predetermined scan conditions to calculate a dose. In this manner, the dose is calculated in consideration of imaging target sizes (see for example, the second to fourth paragraphs of JP-A No. 2004-195121).
Phantom sizes are limited to the above-mentioned two types though imaging targets might be sized variously. The same dose might be calculated for a large person and a small person if they use the same phantom to be applied and the same predetermined scan conditions such as a tube voltage, a tube current, X-ray exposure time, and a helical pitch for helical scanning That is, the dose might not appropriately reflect an imaging target size and might not be calculated correctly.
For this reason, there is a demand to more effectively reflect imaging target sizes on dose calculation performed in an X-ray CT apparatus.